Shallow hardening steel and article thereof



- ity of product.

- Patented Feb; 20, 1945 SHALLOW HABDENING STEEL AND aa'rrcna'rrmanor Janet 2. new, New York, N. Y., are... to

Crucible Steel Company of America, New York, N. Y., a corporation of New Jersey No Drawing. Application August 13, 1941,

Serial No. 406,726 g 2 Claims. (01. 75-123) This invention pertains to improvements in and articles thereof.

The steel of the present invention is extremely shallow hardening and greatly extends the field of utility of such steels as comparedto those previously known. It is particularly adapted for use in relatively thin articles requiring a glasshard'outer surface to resist wear, abrasion, penetration, etc., and a tough inner core to withstand shock, and to prevent cracking in hardening, etc., such as plow shares, small-edged cutting tools, light armor plate, etc. Heretofore, no sufflciently shallow hardening steels have been available for the production of-such articles, and resort has been had to the expedients of surface hardening, viz., carburizing, nitriding, etc., or the use of composite metal for producing the same, but such expedients are both time-consuming and expensive and the results unsatisfactory.

.'I he present invention makes possible, for the first time, the production of these and like articles from shallow hardening steel with accompanying economies in time, expense and superior- Ordinary, plain carbon steels are in general sufficiently shallow hardening for use in articles of relatively thick section of the order of one inch or more. Forthinner sections, however, the steel either hardens' throughout or the desired tough inner "core is of insumcient dimension. Somewhat shallower hardening may be obtained by the additions of .aluminum, or aluminum in conjunction with" vanadium, whereby fshallow hardening effects may be produced in sections somewhat under one inch in diameter, for example, about two-thirds inch or in rare instances,

. shallow hardening steels, and to the production as by restricting the upper limit of elements, such as manganese, which are added to the steel for imparting special properties thereto, such as soundness, workability, etc;

In-order tosecure the preferred results of the invention and'to obtain the desired combination of properties in the steel, such as sufficiently shallow hardening effects, glass-like surface hardness, good core toughness, workability,'etc., the permissible ranges for all of the elements aforesaid are quite critical, although they may be departed from, in greater or lesser degree, parslightly less, but this has been about the lower limit heretofore obtainable.

The present invention greatly extends the pre vious range, and provides excellent shallow hard ening in extremely thin sections of the'material,

- of the order of about one-half to one-quarter inch orlessv in diameter or thickness, as well as improved effects when employed in thicker section, as compared to existing steels.

The improvements brought about by the .present invention are achieved primarily by additions of arsenic to the steel in conjunction with aluminum within specified ranges, and secondarily by restricting'the upper limits of elements-unavoidably present in the steel in small amounts .as impurities, such as'the residual metallic conties as phosphorus, etc., may be present within stituents chromium, nickel, copper, etc., the non-.

metallic inclusions, such as phosphorus, as well tlcularly with increasing thickness, but at some sacrifice to the desirable characteristics.

For imparting the optimum shallow hardening properties consistent with retention of adequate workability and freedom from undue brittleness in the core, arsenic within limits of about 0.02 to 0.50% and preferably within about 0.05 to 0.30%,

should be employed in conjunction with a suitable deoxidizer, .such asaluminum, the latter added in melting within limits of about 8 to- 24 ounces per ton, and preferably within about 10 to 14 ounces per ton.

Carbon should be relatively high for imparting the desired glass-like hardness to the surface,

and will ordinarily lie'within the range of 0.5 to 1.5% and preferably within about 0.9 to about Metallic additions, such .as manganese, and

residuals, such as nickel, chromium, copper, etc.,

are all elements which tend to impart deep hardening properties to the steel, and accordingly must be carefully restricted as to maximum content both individually and in aggregate for imparting optimum shallow hardening properties tothe. steel. Manganese should ordinarily be kept below about 0.5% and preferably under about 0.15% or 0.10%, although insome instances, it may range as high 'as about 0.5 to 0.6%. depending on'the thickness of section to beamployed. Similarly, the residual elements, such as nickel, chromium, copper, etc., should'ordinarily be held under about 0.15% and preferably under about 0.10% for the individual elements, and un-' der about 0.45% and preferably under about 0.25% in aggregate. Such non-metallic-impurithe usual tolerances, for example up to 0.05% of each, although it is preferred that they' do not exceed about 0.03% each.

. Silicon may be present within the usual toler- I ances 'of about 0.1 to 0.5% for 'tool steel. A relatively broad range of analysis in accordance with the invention for imparting shallow hardening properties particularly to thin sections of the steel, is about as follows:'

eJarbom-abcut 0.5 to 1.5% Arsenic-about 0.02 to 0.50% Aluminum (added in melting)about 8 to 24 oz./ton .Manganese-about 0.5% max. Siliconabout 0.1 to 0.5% Nickel-about 0.15% max.

- Chromium-about 0.15% max. Copper-about 0.15% max. Ni, Cr and Cu (in aggregate)about 0.45% max. Phosphorus 0.05% max. Balance iron.

A preferred range for imparting somewhat shallower hardening. is the following:

For imparting optimum shallow hardening, the tollowing range of analysis is preferredz Carbonabout.. '1.15 to 1.25%

Arsenic-about 0.15 to 0.25%

Aluminum (added in melting)-'about.. 12 oz./ton Manganeseabout 0.05% max. Silicon-about 0.1 to 0.2%

Ni, Cr and Cu (in aggre-' gate) -under 0.25% Phosphorus-under 0.03% Sulfurunder. 0.03% Balance iron.

' ton of aluminum added in melting, manganese,

- By way of illustrating the shallow hardenin properties of steel in accordance with the present invention as compared to the best grades of such steels heretofore available, a round bar onehalf inch in diameter and made or a'steel containing about 1% carbon, about 16 ounces per residuals, phosphorus, etc., within usual tolerances, and the balance iron, was found to harden.

throughout on quenching from 1420 I". On the other hand, a bar of steel of similar dimensionsgnog znalysis, except for the addition of about to have an unhar'dened core of about 40% of the diameter of the bar." I

The effect of the residual elements, such as chromium. nickel and copper. on the shallow hardening P perties. of the, steel was determined by a series of tests on specimens made up in the form or slabs each 3'; inch thick. All of these specimens were made or steels containin about 1.2% carbom'about 12 ounces per'ton of aluminum added in melting, and about 0.20501- same, but diflering, however. as regards the amounts of the residuals present. In one of the arsenic, was round on similar quenching the remaining specimens, this limit was exceeded for one or more of these elements. The specimen held within the above limits as to residuals was found on quenching from 1420 F. to have an unhardened core approximately onethird, the thickness of the slab; whereas each of the remaining specimens hardened throughout when similarly quenched. Similar tests, however, conducted on specimens made up into thicker slabs, of the order of 5'; inch or more, demonstrated that the effect of the residuals was relatively unimportant as regards the shallow hardening obtained. Careful regulation of the maximum residual content is therefore of controlling importance primarily in the shallow hardening of extremely thin sections of steel.

The same results werefound to be true as regards variation in the manganese content. This was demonstrated by tests on a series of onehalf inch round bars made of steels containin about 1.3% carbon, 0.15 to 0.25% arsenic, 12 ounces per ton of aluminum added in melting, residuals within usual tolerances, but having manganese contents of 0.33%, 0.48% and 0.71%, respectively. These analyses on quenching in circulating brine spray from 1450 F. were found to have a ratio of unhardened core to diameter of about two-thirds, one-half and zero, respectively. The tests establish, therefore, that for specimens of relatively thick dimensions, of the order of one-half inch or more, that shallow hardening is obtainable with manganese contents as high or about 0.5 to 0.6%. For thinner sections, however, the efiect of manganese is more critical. This was brought out by tests on 512 inch slabs made of steels containing about 1.2% carbon, about 0.12% arsenic, about 12 ounces per ton of aluminum added in melting, residuals within usual tolerances, and otherwise similar analyses with the exception that one specimen contained about 0.2% manganese and the other about 0.04% manganese. The latter specimen was found on quenching from 1420" F. to-have an unhardened core about one-half the thickness of the slab, whereas the specimen containin 0.2% manganese when similarly quenched, was found tohsrden throughout.

.The eflect of varying arsenic additions was demonstrated by a series of tests on one-half inch round here made of steels of varying arsenic content but of otherwise similar analysis, viz., about 1% carbon. about 16 ounces per ton of aluminum added in melting, residuals, manganese, etc, within usual tolerances and the balance iron. These bars were found on quenching to have unhardened cores related to the arsenic content as follows:

Table I I Ratlo 0i unhardened Arsenic addition, per cent core of "diameter 0! be! About .08 13 About .20 .00 About .25 .27

' Arsenic 01 about 0.20%, or within the range of specimens, the residuals were held below the preabout 0.15 to 0.25% taking-melting tolerances into consideration, is thus shown to -provide optimum shallow hardening.

The eflect or varying the. aluminum content was demonstrated by similar tests employing one-half chromium, nickel and copper, whereas in each of {I .lnch round bars eachmade or a steel containing aeeaece 3 to 0.25% about 1% carbon, and residuals, etc., within usual tolerances, but diflering as to aluminum. Thesebars were found on quenching to have unhardened cores related to thealuminum addition as follows:

Table II Ratio of unhardened Aluminum added in melting, ozJton core to diameter of bar Thus the optimumaluminum addition is about 12 ounces per ton.

It was shown, by similar tests, that increasing additions of phosphorus noticeably impaired the shallow hardening properties of the steel, and that best results are obtained by holding these elements within the limits above stated. And the same applies as regards silicon. i

The steel in accordance with the invention is preferably made from selected base material which is low in nickel, chromium, copper, phos- .arsenicwithin the optimum limits of about 0.15

1. An alloy steel, characterized by extremely shallow hardening properties, and containing:

about 0.5 to 1.5% carbon, about 0.02 to 0.59;

arsenic, about 8 to 24 ounces per ton of aluminum added in melting, ,rnanganese and residual elements within commercial tolerances, and the baiance substantially all iron.

2. A shallow hardened article made oi an alloy steel containing: about 0.5 to 1.5% carbon. about 0.02 to about 0.5% arsenic, about 8 to 24 ounces per ton of aluminum added in melting, manga nese and residual elements within commercial tolerances, and the balance substantiall all iron.

JANET Z. BRIGGS, 

